The invention relates to electronic article surveillance markers of the type used with optically recorded media for use with magnetic-type electronic article surveillance systems.
Magnetic-type electronic article surveillance (xe2x80x9cEASxe2x80x9d) systems are widely used to inhibit the theft of merchandise such as clothing, books, cassettes, and compact discs. EAS systems are often used to prevent the unauthorized removal of articles from a protected area, such as a library or retail store. An EAS system usually includes an interrogation zone or corridor located near the exit of the protected area, and markers or tags attached to the articles to be protected. EAS systems have been based on magnetic, RF, microwave, and magneto-strictive technologies, but regardless of the particular technology involved, the systems are designed such that the tag will produce some characteristic response when exposed to an interrogating signal in the corridor. Detection of this characteristic response indicates the presence of a sensitized tag in the corridor. The EAS system then initiates some appropriate security action, such as sounding an audible alarm, locking an exit gate, or the like. To allow authorized removal of articles from the protected area, tags that are either permanently or reversibly deactivatable (referred to as xe2x80x9csingle-statusxe2x80x9d and xe2x80x9cdual-statusxe2x80x9d markers, respectively) are often used.
Although EAS markers have been in use for the theft protection of optically recorded media such as compact discs and CD-ROMs, the markers have generally been adapted for attachment to the packages containing new compact discs and have been poorly suited for direct attachment to the disc itself. One solution to this problem is posed in coassigned U.S. Pat. No. 5,699,047 (Tsai et al.) and U.S. Pat. No. 5,825,292 (Tsai et al.), which describe a marker including one or more marker elements attached to a flexible support sheet. The support sheet (or in one embodiment only the marker elements) may be adhered to the optical disc such that the marker elements are symmetrically spaced with respect to the center of the disc, to avoid upsetting the balance of the disc when it is rotated. However, as ever greater amounts of information are stored on a single optically-recorded disc, manufacturers have sought to record on both sides of that disc. Thus, any marker element that covers an area of the disc where optical information is or may be recorded and must be read can be undesirable.
U.S. Pat. No. 5,347,508 (Montbriand et al.) discloses another style of EAS marker in combination with an optical disc. The marker, in the form of a ring, comprises concentric signal-producing and signal-blocking layers that combine to provide a dual-status marker that can be embedded into a circular channel formed near the center of the disc. The marker disclosed in this patent used a contiguous signal blocking layer, and the bias field from that signal blocking layer provides the deactivation mechanism. Although having its own utility, EAS markers of the type disclosed in Montbriand et al., with a contiguous signal blocking layer, may not be sufficiently effective in deactivating the marker under all circumstances.
In view of the foregoing, it would therefore be desirable to provide an EAS marker that overcomes the disadvantages of conventional EAS markers for optically-recorded media.
The present invention includes within its scope an electronic article surveillance marker comprising a signal producing layer including flux collection portions joined by magnetic switching sections, and a signal blocking layer comprising signal blocking elements overlying each flux collection portion, the elements each having at least one boundary that overlies a magnetic switching section. In a preferred embodiment, the magnetic switching sections each have a major axis A, and the signal blocking elements each have at least one boundary that overlies a magnetic switching section and has a tangent T that is not perpendicular to the major axis A of that magnetic switching section. The marker preferably is suitable for use on an optical disc, though it may be used on other articles as well.
Methods of making the inventive marker are also disclosed, including by making the signal producing layer and the signal blocking layers separately and laminating them together, or by chemically etching away from a substrate the materials of each layer that are not required.